Electrochemical process for production of sodium perchlorate



PatentedJana 1946 ELECTROCHEDIICAL PROCESS :Fofi- 1986- DUCTION OF SODIUM PEBGHLORATE Joseph B. Ryan, Williamsville, N.Y., assignor. to a Buffalo Electro-Chemical Company, 1110., Buffalo, N. Y.

No Drawing. Application Mai-ch20, 1943,

Serial No. 479,905 1 Claim. 10!. 294-42) The present invention relates to the manufacture of sodium perchlorate in a relatively pure condition and free from contamination with lower oxy acids of halogens. a

Sodium perchlorate is an excellent source of oxygen in explosive mixtures possessing high detonating and shattering power and, in the dry condition, is extremely useful in this connection.

- However, the presence of minute amounts of unconverted chlorate in the perchlorate increases of'chlorate that is economically feasible. The 'economic limit is reached whena concentration of about 1 to 5 grams per liter chlorate is reached. This-is due to the fact that thehigh current density of 450 amperes per square foot proddces excessive quantities of ozone by reason of electrolysis of the aqueous electrolyte, thus lowering the cell efliciency.

the sensitivity of the perchlorate to heat and to shock. It is an object of the present invention to manufalcture pure sodium perchlorate free of halogen oxy acids or salts thereofu -It is also an object of the present invention to produce sodium perchlorate directly from sodium chlorate while, at the same time, eliminating ex cess of chlorate or avoiding the presence of chlorate in the perchlorate produced.

In accordance with the present invention, therefore a cell solution of sodium chlorate is oxidized anodically, in the usual way, in a conventional oxidation cell well knownfor this purpose. Thus, a cell solution is prepared containing about 700'grams per liter sodium chlorate. To this solution there is added about 2 grams pr liter ofsodium chromate o ornate. The purpose of the chromate protec the cathode and to prevent the i0 ation in solution of reducing hydrogen, from electrolysis of the aqueous The perchlorate cell solutionat the end of the conversion is, in accordance with the present invention, already at a relative elevated temperature, namely, in the neighborhood of about 60 C.

To this solution, removed from the cell, a substance is added having the power of selectively reduclng 'any residual chlorate and chromate. The reducing material .selected must possess, in

' addition to this selective reducing power, the .characterlsticof ready removability'from the solution. Sulfur dioxide provides an excellent reducing substance forthe purpose intended, since this material may be bubbled through the elec- "trclyzed cell solution, destroying the residual chlorate which is normally present'at this point to the extent of about one gram per liter, and reducing any portion of the chromate not already reduced at the cathode. The chlorate is reduced electrolyte with destruction of some of the chlorate in the cell and, therefore, at a' reduced cell efllciency of output. 7 a

This solution is electrolyzed in the usual-way and generally in a conventional 'cell cascade. The operating voltage and amperage will depend upon the construction of ,the cell and the movement ofelectrolyte therethrough. However, these are factors which are well known in the art and con stitute no part of the, invention herein described and claimed. In general, the temperature is permay reach 60 C. At this point, the cell electrolyte contains about 840. grams per liter sodium perchlorate. This figure may be increased to a limiting value of about 1100 grams per liter by adding additional sodium chlorate to the electrolyte from two-thirds to half way through the cascade to compensate for the sodium chlorate already'converted to perchlorate. However, as

' to chloride, and the chromate to chromic compounds;

The sulfur dioxide treatment is continued until such time as the cell solution gives no. further test for the presence of chlorate ion. To this end, the electrolyzed cell solution is added to a test indicator made of one gram per liter indigo carmine. The test is made by mixing one milliliter of the indigo carmine with 5 milliliters of concentrated hydrochloric acid, and the mixture mitted to rise in the last cell of the cascade and the presence of unconverted chlorate in perchlorate imparts very serious and undesirable char- 1 acteristics to the completed product, it is preferable o op ryte the cell to the lowest concentrationv heatedto boiling. To this boiling mixture, 5 milliliters of the reduced cell solution are added. Five parts per million of chlorate will cause a sharp decoloration of the indicator, and one part per million can be detected. Sulfur dioxide does not interfere with this procedure. Sulfur dioxide is, therefore, added to this solution until a test made with the indigo carmine indicator shows the presence of less than one part per million of chlorate, that is, the elimination of substantially all of the chlorate and any other halogen oxy acids.

Excess sulfur dioxide is eliminated from the treated solution by heating the solution to boiling, and bubbling air therethrough to sweep out such excess. Sulfur dioxide may be tested for by permitting the evolved vapors to act upon Mo N potassium permanganate solution.

The acidity of the treated solution is then adcarbonate solution or other mild alkali may be employed. The chromic ion isprecipitated as chromic hydroxide and may be removed.

The cell solution thus urified is evaporated to dryness and the. sodium perchlorate dried carefully and slowly iat;about180 C." ,Ihefmateriai may be dried in any suitl le or conventional fashion by the employment of conventional pulyerizing and drying equipment and, in general,

the time required to dry the. materialjwiil be" dependent directly upon the "eiiieiency or'the drying equipment.

An analysis of the dried perchlorate gave the following composition:

Y P r Sodium perchlorate 98.70 Sodium sulfate- 1.00 Sodium chloride "0.04 Sodium carbonate 0.32

me present invention provides a method oi purifying electrolyzed chlorate and-the j a 02,709 iusted to a'pl-I ofabout fl. To this end, sodium production or sodium perchlorate tree of deleterious chlorate whereby the sodium perchlorate may be used directly as a compounding agent in' explosive materials without the necessity of precipitated chromic hydroxide, and thereafter changing the perchlorate to the potassimn-or ammonium salt as has beendone heretofore. -whatis claimed is: a The method of manufacturing solid sodium iur dioxide to reduce chromates to chromic salts and the, residu'aLchlorate to chloride, adding mild alkali t'oadjust the pH of the solution to about 7 to precipitate chromic hydroxide, removing the evaporating and drying the relatively purified solution to recover the-sodium perchlorate.

JOSEPH R. RYAN. 

